1. Technical Field
The present invention relates to a virtual image display system such as a head-mounted display mounted on a head.
2. Related Art
Recently, as virtual image display systems that enable formation and observation of virtual images like head-mounted displays, various systems of a type of guiding image light from a display device to an eye of an observer using a light guide plate have been proposed.
In the virtual image display systems, for superimposition of image light and external light, see-through optical systems have been proposed (see Patent Document 1 (JP-A-2006-3879) and Patent Document 2 (JP-A-2010-224473)).
However, in the system described in Patent Document 1 and the like, seeing through is realized by an eye division method using a light guide optical system having a smaller output aperture than the eye size, and it is difficult to make the display size of the virtual image larger. Further, since the light guide optical system smaller than the eye size is used, it is difficult to make the effective pupil diameter (lighting diameter that enables introduction of virtual images, also referred to as “eye ring diameter”) for matching with the individual pupil distances of humans. Furthermore, since the output aperture and the casing of the light guide optical system is placed physically near the eye, a blind spot is produced and seeing through is not complete.
Note that, as an optical system for head-mounted display, there is one having a light guide pipe that may advance plural light modes having different light guide angles (see Patent Document 3 (JP-A-2008-535001)). It is conceivable that a see-through display system is formed by using a half mirror as the third optical surface at the output side and making the transmitted light through the third optical surface travel straight (for example, adding a prism) in the optical system.
However, in the optical system in Patent Document 3, on the assumption that images by plural light modes are misaligned with one another, a liquid crystal panel is illuminated by collimated lights set at different incident angles with respect to each light mode. Further, by changing the display contents in the respective light modes and sequentially executing displays of the respective light modes, the images of the respective light modes are joined and a whole image is obtained. In this case, one liquid crystal panel should display the center image and the right and left images forming the whole image while changing them with time differences, and the virtual image display system becomes complicated and the images for observation become darker.
Besides, a virtual image display system that enables observation of virtual images by superimposition on external light using a light guide member having a light-exiting part covering the view without necessity to join the images with time differences is conceivable, however, it is not easy to display a large image, and, when a member such as a prism for seeing through is connected to the light guide member, ghost light is generated by the member and the ghost light becomes easier to reach.